Method and device for passing a web in connection with a finishing device of a paper or board machine

ABSTRACT

A web (W) is passed from a preceding treatment stage to a finishing device in which the web (W) is finished in the finishing device and from which finishing device the web (W) is passed further to a subsequent treatment stage. The web (W) is brought to a roll ( 11; 14 ) of the finishing device as supported substantially before a nip area (N 1 ; N 2 ). The web (W) is passed from the circumference of a roIl ( 12; 15 ) of the finishing device as substantially supported afler the nip area (N 1 ; N 2 ). A device for passing a web in connection with a finishing device of a paper machine causes a web (W) to be brought by the device to the circumference of a roll ( 11; 14 ) of the finishing device substantially before a nip area (N 1 ; N 2 ) and/or the web (W) can be passed from the circumference of a roll ( 12; 15 ) of the finishing device substantially after the nip area (N 1 ; N 2 ).

CROSS REFERENCES TO RELATED APPLICATIONS

This application is a U.S. national stage application of InternationalApplication No. PCT/FI01/01008, filed Nov. 21, 2001, and claims priorityon Finnish Application No. 20002550, filed Nov. 21, 2000, the disclosureof each application being hereby incorporated by reference herein.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH AND DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

As known in the state of the art, free draws have been used in papermachines when passing a paper web from one treatment stage to the next.The general trend today is that attempts are being made to pass thepaper web as supported from one treatment stage to the next, and thedevelopment has indeed moved forward so that the wet end and the dryersection of the paper machine have for the most part been provided withmeans so that the transfer of paper is supported over the entiredistance. However, in finishing there are stages in which unsupportedruns of the web are still used at present, for example, in connectionwith calenders or on-line coating devices. Since the current trend isalso that finishing devices are connected as on-line units to the papermachine, the significance of web support matters for the efficiency ofthe total line is greater than before when using off-line furthertreatment units. Since all unit process devices are in the same chain,the problems presented by free draws in the transfer of the web andpossible web breaks cause problems to the entire line and may cause evena shutdown of the entire line.

Today's paper machines also aim at an increase of speed and decrease ofthe basis weight of the paper web as well as at higher efficiencyrequirements. Thus, unsupported runs cause problems, and therefore theirelimination is very important.

Thus, it is an object of the invention to provide a method and a devicein connection with which the run of the web is supported in connectionwith a finishing device.

With respect to the state of the art associated with the invention,reference is made to FI patent application 973725 which discloses anarrangement in which a web is conveyed by means of a support wire orequivalent to a multi-nip calender from the last drying cylinders placedsubstantially higher than the other cylinders of a dryer section, onwhich support wire the web is passed to the first pre-nip of thecalender formed between the topmost calender roll and a belt calenderroll or a wire guide roll.

An arrangement is known from the state of the art in which a paper webis passed as a supported run through a calender supported by a supportmember which has been guided to run through a calendering nip of thecalender. In this respect, reference is made to FI patent 95 061. Aproblem in this prior-art arrangement is that the support member ofpaper influences the process itself and thus also the quality of thepaper being manufactured as the support member runs through the nip.Further, this restricts the selection of the support member material tobe used because the support member thus takes part in the process, whichmeans that the material of the support member shall be selectedaccording to the demands of the process and the process parameters shallbe adjusted taking account of the effect of the support member.

SUMMARY OF THE INVENTION

It is thus a particular object of the invention to provide a fullysupported run of the paper web in connection with a finishing device,which does not affect the manufacturing process itself, nor the qualityof the paper that is manufactured.

In accordance with the invention, a web, in particular a paper or boardweb, is brought to the circumference of a roll in a finishing device assupported substantially before the nip area and the paper web leaves thecircumference of the roll of the finishing device and is passed to besupported by means of a support member substantially after the nip area.In accordance with the invention, the paper web is brought to thefinishing device while supported by a support member, for example, abelt, a felt or a wire or equivalent such that the transfer is supportedover the entire distance from a preceding treatment stage to saidfinishing stage, during it and after it further to the followingtreatment stage after it.

In accordance with the invention, a support member loop is used inconnection with which two or more rolls have been arranged to guide it,and onto which support member a paper web is passed and on support ofwhich support member the paper web is conveyed into connection with aroll of a finishing device substantially before the nip of the finishingdevice and, in a corresponding manner, the web is passed by means of asupport member loop from a roll of the finishing device to furthertreatment. The support member runs past the roll substantiallytangentially to the roll of the finishing device.

The invention is particularly suitable for use in connection withcalenders, in particular soft calenders, in which connection it alsoprovides the advantage that, when the support member is placed such thatthe paper web to be calendered is guided to run on the circumference ofa thermo roll before a nip, the paper web and also the support memberfor its part form a shield which prevents the heat of the thermo rollfrom evaporating into the surroundings, with the result that the heat ofthe thermo roll is transmitted to the paper. By this means, the web canbe passed to the nip while it is hot and the heat of the thermo roll canbe utilised with a greater efficiency than in the arrangements knownfrom the state of the art.

The apparatus in accordance with the invention has been placed inconnection with a finishing device and the process stage preceding it isconstituted by, for example, a dryer section or a coating unit and it isfollowed by, for example, a reeling or coating unit and, in accordancewith the invention, the web runs from the preceding process stage to thesubsequent process stage through the process stage in question assupported all the time by means of support members and the rolls used inthe process stages.

The support member according to the invention is formed of a loop-shapedsupport member which is guided by two or more rolls, and one or moresupport member units have been arranged in connection with a finishingdevice to support the web.

When, in accordance with the invention, the run of the web has beenprovided as supported in connection with a finishing device, it ispossible to raise the speed of the paper machine and use paper gradeshaving a lower basis weight. Thereby, a greater efficiency is achievedon the paper machine. A supported run is not so susceptible to webbreaks and other disturbances, whereby substantial benefits are achievedin the entire on-line process.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in more detail withreference to the figures of the accompanying drawing, to the details ofwhich the invention is, however, not by any means meant to be narrowlyconfined.

FIG. 1 is a schematic view of one application of the invention inconnection with a two-nip soft calender.

FIG. 2 is a schematic view of one application of the invention inconnection with a one-nip soft calender.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As shown in FIG. 1, a paper web W is brought by a support member 10 to aSym-roll 11 of a soft calender, from which it is passed along the roll11 into a calendering nip N1 and further from the surface of a thermoroll 12 by means of a support member 13 to a Sym-roll 14 of a subsequentcalendering nip N2 and further to a thermo roll 15, from which it ispassed by means of a support member 16 to further treatment, forexample, to a reel-up. Thus, a loop-shaped support member 13 has alsobeen disposed in connection with the run between the calendering nipsN1, N2, on which support member the web W is passed as supported from,for example, a thermo roll of the calendering nip N1 to, for example, aSym-roll of the following nip N2.

As shown in FIG. 2, a paper web W is passed from a dryer section 40 of apaper machine to a support belt 20, by means of which said web W istransported to a thermo roll 21 of a calender and passed along itssurface to a calendering nip N3 and further along the surface of aSym-roll 22 to a second support belt 23, which has been placed above thepaper web W and in connection with which, for example, blow suctionboxes 24, 25 have been arranged to support the run of the web W. Afterthat, the web W is passed by means of a roll 26 to further treatment.

As shown in FIGS. 1 and 2, a support member unit 30 comprises a supportmember 10, 13, 16, 20, 23, for example, a belt, a wire, a felt orequivalent, which has been arranged to run in a loop-like fashion whileguided by guide rolls 33. Depending on the application, two or moreguide/alignment rolls 33 have been arranged in connection with eachsupport member 10, 13, 16, 20, 23.

As illustrated in FIGS. 1 and 2, the paper web W is passed to thecalender substantially before the calendering nip N1; N2; N3 by means ofthe support member 10; 13; 20 and the web W is passed away from a rollof the calender substantially after the nip N1; N2; N3 and passed tofurther treatment by means of the support member 13; 16; 23. It shall beparticularly noted that the support member does not take part in theprocess because it does not run through the calendering nip N1, N2, N3,but, instead, the support member brings the web W substantially close tothe nip to the circumference of the roll defining the nip and, in acorresponding manner, the support member receives the web substantiallyafter the nip from the circumference of the roll defining the nip.

Above, the invention has been described with reference to only some ofits advantageous application examples, to the details of which theinvention is by no means meant to be narrowly confined.

1. A method for passing a web in connection with a calender of a paperor board machine, comprising the steps of: passing the web from apreceding process stage on a first support member loop which carries theweb from the preceding process stage to a first roll of the calender,the first roll having a circumference and forming a first nip with asecond roll; supporting the web on the first support member loop priorto being passed to the first roll and passing the web to the first rollcircumference substantially before the first nip such that the firstsupport member loop does not pass through the first nip; passing the webfrom the circumference of the first roll to the first nip definedbetween the first roll and the second roll of the calender; andcalendering the web at the first nip, and passing the web along acircumference of the second roll between the first nip and a secondsupport member loop from which the web is transferred to a subsequentprocess stage; wherein one of the first roll and the second roll is athermo roll and the web is wrapped about a portion of the thermo roll toform a shield so preventing loss of heat from said thermo roll; andwherein the web runs from the preceding process stage to the subsequentprocess stage through the calender while being supported all the time bythe first support member loop, the first calender roll, the secondcalender roll and the second support member loop.
 2. The method of claim1 wherein one of the first roll and the second roll is a soft roll sothat the web is calendered in a soft calender.
 3. The method of claim 1,further comprising the steps of passing the web from the second supportmember loop to a second calender having a third roll, and from the thirdroll to a fourth roll of the second calender which defines a second nipwith the third roll, and from the fourth roll to a third support memberloop, wherein no support member loop passes through a calender nip. 4.The method of claim 1, wherein the first support member loop has a runwhich is guided by two or more rolls.
 5. The method of claim 1, whereinthe first support member loop runs past the first roll tangentially tothe first roll.
 6. A calender apparatus in a paper or board machine, theapparatus comprising: a first support member which carries a web from apreceding treatment stage; a first roll which receives the web from thefirst support member; the first roll having a circumference and forminga first nip with a second roll, wherein the web is supported on thefirst roll circumference substantially before the nip, and travelsthrough the first calendering nip, and wherein the first support memberdoes not pass through the first calendering nip; a second support memberwhich receives the web from the second roll after the first calenderingnip; a third roll which receives the web from the second support member;a fourth roll which forms a second calendering nip with the third roll,wherein the second support member does not extend through the secondcalendering nip.
 7. The apparatus of claim 6 wherein the calender is asoft calender and one of the first roll and the second roll is a thermoroll.
 8. The apparatus of claim 6 wherein the second support membercomprises a support member loop having at least two rolls disposedwithin the loop which guide the support member loop.
 9. The apparatus ofclaim 6 wherein the second support member has portions which runtangentially to the second roll.
 10. The apparatus of claim 6 furthercomprising a third support member which receives the web after thefourth roll and passes the web to a subsequent treatment stage.
 11. Acalender apparatus in a paper or board machine, the apparatuscomprising: a support member loop formed from a belt, wire, or felt; afirst calender roll, having a circumference; a second calender rollhaving a circumference and forming a calender nip with the firstcalender roll; a paper or board web extending along the support member,and on to the circumference of the first calender roll, and wherein thesupport member loop is spaced from the calender nip, the web extendingalong the first calender roll circumference and passing through the nipand extending along a circumference of the second calender roll; and asecond support member loop formed from a belt, wire, or felt, the webextending from the second calender roll to the second support memberloop, wherein the first calender roll and the second calender roll forma soft calender with one thermo roll.
 12. The apparatus of claim 10further comprising; a third calender roll and a fourth calender rollforming a second nip and a second soft calender having one heated thermoroll; and wherein the third calender roll is tangent to the secondsupport member loop, and the web extends along the second support memberloop, the third calender roll, and through the second nip and along thefourth calender roll to a third support member loop formed from a belt,wire, or felt,which is tangent to the fourth roll.
 13. The apparatus ofclaim 11 wherein the support member loop is tangent to the firstcalender roll; wherein the second support member loop is tangent to thesecond calendar roll.